We propose an improvement of the interferometric method used up to now to measure the chromatic dispersion in single mode optical fibers, which enables dispersion measurements in higher-order modes ...over a wide spectral range. To selectively excite a specific mode, a spatial light modulator was used in the reflective configuration to generate an appropriate phase distribution across an input supercontinuum beam. We demonstrate the feasibility of the proposed approach using chromatic dispersion measurements of the six lowest order spatial modes supported by an optical fiber in the spectral range from 450 to 1600 nm. Moreover, we present the results of numerical simulations that confirm sufficient selectivity of higher-order mode excitation.
We demonstrate a fiber-based optical vortex beam source operating in broadband or tunable mode in the spectral range of 1100–1400 nm. The vector vortices of the total angular momenta equal to +2, 0, ...and −2 are obtained by converting the respective linearly polarized (LP
11
) modes of the two-mode birefringent PANDA fiber with stress-applying elements by gradually twisting its output section. At the input end, the PANDA fiber is powered by broadband supercontinuum or tunable Raman solitons generated in the LP
11
polarization modes of a birefringent microstructured fiber with a specially designed dispersion profile and coupled to the respective LP
11
modes of the PANDA fiber. Two pulse lasers operating in different regimes (1 ns/1064 nm and 190 fs/1037 nm) were used as the pump to generate supercontinuum or tunable solitons directly in the LP
11
modes of the microstructured fiber purely excited with a special Wollaston prism-based method. The high modal and polarization purities of the beams after successive transformations were experimentally confirmed. We also proved the vortex nature of the output beams using shearing interferometry.
The cover image presents the first stand‐alone telecom quantum light source launching single photons directly into a single‐mode optical fiber. It includes a semiconductor quantum dot (QD) which is ...excited by an integrated laser and cooled by compact Stirling cooler at 40 K. The advanced quantum device includes all filter elements to suppress intensive laser light and to direct single photons at a wavelength of 1.3 µm to the output. For further details see article number 2000018 by Stephan Reitzenstein and co‐workers.
We present a novel method for determining chromatic dispersion profile from a broadband spectral interferogram obtained by using a white-light interferometry technique. The proposed method is based ...on direct calculations of a second derivative of the registered spectral intensity at extremal points, which in result gives a spectral phase difference derivative further used for dispersion determining. Although the method is best suited for processing interferograms with modulation around a zero level (zero-mean value interferograms) and slowly changing envelope, the conducted numerical tests show that it is highly tolerable to different types of perturbations of the input interference signal. The proposed method can be applied both to spectral interferograms with monotonically changing phase difference as well as containing stationary phase difference points. We demonstrate the effectiveness and accuracy of the proposed method in measurements of chromatic dispersion of commercially available samples like the BK7 glass plate and the Corning SMF-28 optical fiber.
We report on a new phenomenon of light guidance in a fiber core created by an arrangement of holes making a partially open ring. In such structure there is no complete refractive index barrier to ...confine the light and therefore it cannot guide light if untwisted. However, if the open ring of holes is shifted off the symmetry axis of the twisted fiber then the mode confinement and low loss propagation is possible due to purely geometrical effect related to the increase in the optical path of light following the helical route. Properties of such structures, including confinement loss, modal field distribution, birefringence of fundamental modes were investigated both numerically and experimentally. We also studied the effect of bending, which leads to periodic modulation of the propagation characteristics of the twisted fiber. Furthermore, we demonstrate a possibility of displacement measurements based on bend-induced loss using some of the fabricated fibers, in which the sensitivity to bend is controlled by a twist rate and core structure.
This study investigated the nonlinear frequency conversions between the six polarization modes of a two-mode birefringent fiber. The aim was to demonstrate that the selective excitation of different ...combinations of linearly polarized spatial modes at the pump wavelength initiates distinct intermodal vector four-wave mixing processes. In particular, this study shows that exciting two orthogonally polarized LP01 and LP11 modes can result in simultaneous generation of up to three pairs of different spatial modes of orthogonal polarizations at different wavelengths. The role of the phase birefringence of the spatial modes in the phase-matching of such a four-wave mixing process was explained. Moreover, the theoretical predictions were verified through numerical simulations based on coupled nonlinear Schrodinger equations and also confirmed experimentally in a commercially available birefringent fiber.
Deterministic solid-state quantum light sources are considered key building blocks for future communication networks. While several proof-of-principle experiments of quantum communication using such ...sources have been realized, most of them required large setups often involving liquid helium infrastructure or bulky closed-cycle cryotechnology. In this work, we report on the first quantum key distribution (QKD) testbed using a compact benchtop quantum dot single-photon source operating at telecom wavelengths. The plug\&play device emits single-photon pulses at O-band wavelengths (\(1321\,\)nm) and is based on a directly fiber-pigtailed deterministically-fabricated quantum dot device integrated into a compact Stirling cryocooler. The Stirling is housed in a 19-inch rack module including all accessories required for stand-alone operation. Implemented in a simple QKD testbed emulating the BB84 protocol with polarization coding, we achieve an antibunching of \(g^{(2)}(0) = 0.10\pm0.01\) and a raw key rate of up to \((4.72\pm0.13)\,\)kHz using an external pump laser. In this setting, we further evaluate the performance of our source in terms of the quantum bit error ratios, secure key rates, and tolerable losses expected in full implementations of QKD also accounting for finite key size effects. Furthermore, we investigate optimal settings for a two-dimensional temporal acceptance window applied on receiver side, resulting in predicted tolerable losses up to \(23.19\,\)dB. Not least, we compare our results with previous proof-of-concept QKD experiments using quantum dot single-photon sources. Our study represents an important step forward in the development of fiber-based quantum-secured communication networks exploiting sub-Poissonian quantum light sources.
A user-friendly fibre-coupled single-photon source operating at telecom wavelengths is a key component of photonic quantum networks providing long-haul ultra-secure data exchange. To take full ...advantage of quantum-mechanical data protection and to maximize the transmission rate and distance, a true quantum source providing single-photons on demand is highly desirable. We tackle this great challenge by developing a ready to use semiconductor quantum dot (QD)-based device that launches single photons at a wavelength of 1.3 um directly into a single-mode optical fibre. In our approach the QD is deterministically integrated into a nanophotonic structure to ensure efficient on-chip coupling into a fibre. The whole arrangement is integrated into a 19" compatible housing to enable stand-alone operation by cooling via a compact Stirling cryocooler. The realized source delivers single photons with multiphoton events probability as low as 0.15 and single-photon emission rate up to 73 kHz into a standard telecom single-mode fibre.
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